MORÓN, Spain -- Marines can fight from the air, the land, and the sea. But can they swim?

The commandant isn't so sure.

During a brief visit to Marines assigned to the Corps' crisis response force for Africa in Moron, Spain, in December, Gen. Robert Neller said he wants to make proven swimming skills a requirement or contributing factor for promotion.

The revelation came just days after the Marine Corps announced, at Neller's direction, the return of the Battle Skills Test, another promotion requirement that will ensure Marines can accomplish essential tasks such as applying a tourniquet or employing a map and compass.

"I know nobody wants to have another requirement," Neller said of the prospective swimming obligation. "[But] it's either that or accept the fact that somebody might go into the water off a ship or off an airplane and they drown."

In an interview, he told Military.com that the idea to implement a more rigorous swimming requirement had come to him after Marines were lost in late July 2017 when the MV-22 Osprey carrying them went down off the coast of Australia.

"We lost three Marines in that crash," Neller said. "I don't think it was because they couldn't swim. But ... we teach everybody basic life-saving or basic swimming at recruit training, but we never test again. So why don't we test?"

The Marine Corps and Navy take similar approaches to swimming requirements. Both services require a basic swimming competency for all recruits at entry-level training.

For Marine recruits, the minimum requirement is call water survival basic. It requires Marines, clad in cammies and boots, to strip off protective gear, including body armor and a rifle, while in the water under 10 seconds; jump into the pool from a 15-foot tower and swim 25 meters in deep water; employ a floatation device made from a pack; tread water for four minutes, and complete another 25-meter pack swim. This qualification is good for two years and must be renewed when it expires.

For the Navy, the minimum third-class swim test requires that a recruit can swim 50 yards, complete a deep-water jump, do a five-minute prone float, and inflate clothing to float with. A sailor can also choose to incorporate a 500-meter swim as part of the annual physical readiness test.

For both services, there are more advanced qualifications that can be obtained. But unless Marines enter a more specialized role, such as reconnaissance, swimming qualification ends there.

For the Marine Corps, making swim skills a more regular requirement would mean ensuring that every service installation has a usable pool, and that every Marine has access to one.

"Part of the problem is, what do you do with people who are on recruiting duty or independent duty or the reserves?" Neller said in the interview. "How do you do that? So I don't have a detailed plan yet."

But, he added, he isn't planning to give up on the goal just because it might require effort and money to execute.

If the plan does move forward, it's not clear yet what skills Marines will have to demonstrate or how it will be incorporated into requirements. Neller expressed interest in making swim skills part of a Marine's cutting score, the number that signals a Marine's eligibility for promotion to corporal or sergeant.

"If you add it to cutting score, it incentivizes it," he said. "If you're not qualified for promotion unless you can swim, or you're more qualified if you're a better swimmer ... There's a whole lot of things going on, there's a whole list of things we're trying to do, and we'll have to poke on this one again to see where we are."

One thing is clear, however: Neller wants Marines to be ready.

"If there's a pool here and you're not a good swimmer," he told the Marines, "you've got to get your butt in the pool."